David Cameron will today declare that he is opposing the alternative vote from gut instinct as much as from rational argument, as he goes head to head on the issue of voting reform with Ed Miliband.

The prime minister and the Labour leader are due to make speeches on the subject at rival events at almost the same time. With coalition and Labour splits on full display, Cameron will be joined by John Reid, the former Labour home secretary, while Miliband will be accompanied by Vince Cable, the business secretary.

Cameron has not shared an anti-AV platform with a Labour politician before and he will insist that he and Reid "don't agree on much". Reid is expected to reciprocate the sentiment, but will say "some issues are so important that they transcend party politics" and that he and Cameron are opposed to AV because they are "united in believing that politicians are the servants of the people".

Writing in today's Independent, the Labour leader, meanwhile, characterises the AV contest as a "choice coming down to hope versus fear", and accuses Cameron of making baseless negative claims about the system.

The campaign has, at times, become particularly acrimonious, with Lord Ashdown, the former Lib Dem leader, accusing George Osborne and other Tories campaigning for a no vote in the AV referendum of "cynical smears and scaremongering". But the party leaders are expected to seek to raise the tone of the debate by focusing more on the respective merits of their favoured systems.

Miliband writes today: "[The Tories] claim [AV] will somehow help extremist parties; quite the opposite, given the need to gain more votes from a wider spectrum of opinion to win a seat. Little wonder the BNP wants people to reject change."

He said that the current system, first past the post, give parties no motivation "for pretending anything other than that they hate each other equally". No reason to find points of common ground; just to disagree.

"To secure a majority of votes under AV, candidates will need to be more honest about points of agreement."

Cameron, claiming the debate on AV too often involves "a language of proportionality and preferences, probabilities and possibilities", will say: "For me, politics shouldn't be some mind-bending exercise. It's about what you feel in your gut – about the values you hold dear and the beliefs you instinctively have. And I just feel it, in my gut, that AV is wrong."

He will argue that AV will take power away from the people, "damage our democracy permanently" and lead to more hung parliaments.

This assertion was disputed by the deputy prime minister, Nick Clegg, who told the BBC's Politics Show that AV would not lead to more coalition governments. "More hung parliaments have been delivered under first past the post than have been delivered under AV in Australia," the Lib Dem leader said. But Cameron said the coalition would survive, whoever won the referendum: "Whoever is on the losing side, as it were, will just have to pick themselves up and say: well, it was a fair argument, a fair fight, a fair referendum, the country has decided and now we have to get on with all the things that really matter so much."

Cameron also found himself defending his chancellor after Osborne was singled out for attack in a particularly strongly worded article by Ashdown. Osborne infuriated AV campaigners last week by suggesting the Electoral Reform Society should not be funding the yes campaign because its subsidiary, Electoral Reform Services Ltd, a company that organises elections, could profit from a switch to AV.

The ERS says it is completely untrue but Five days ago, lawyers for the ERS sent a letter to journalists saying that although ERSL makes money from election administration, the type of election system used is "entirely irrelevant" to the provision of these services and "a change in the voting system would, therefore, have absolutely no impact on any of the revenue earned by the ERSL."

Osborne said its involvement in the funding of the yes campaign "really stinks", prompting Ashdown to accuse him and other anti-AV campaigners in an article in the Observer of resorting to "smears, deliberate misrepresentations and sometimes even downright lies".

In an interview on Sky News, Cameron said: "The point George Osborne made, that the Electoral Reform Society is a big funder of the yes campaign, that it has an organisation that could make money out of it, that's a fact, and I think there's nothing wrong with bringing that fact out." But although this seemed potentially provocative, Ashdown subsequently praised the prime minister for focusing in his Sky interview largely on the substantial issues at stake in the campaign.

Cameron also insisted that the coalition would survive whoever won the referendum.

"Whatever the result on May 5, this is a five-year government, Nick [Clegg] and I are absolutely committed to taking the government and its programme forward," he said.

"Whoever is on the losing side, as it were, will just have to pick themselves up and say: well, it was a fair argument, a fair fight, a fair referendum, the country has decided and now we have got to get on with all the things that really matter so much."

Migration divisions

Nick Clegg highlighted continuing coalition divisions over immigration on Sunday by claiming that the government is not pursuing a "fixed numerical target" for the number of people coming to Britain every year.

The deputy prime minister repeatedly refused to say that he agreed with David Cameron that the government was aiming to reduce the level of net migration from hundreds of thousands a year to tens of thousands a year.

In his speech last week Cameron said he believed that government immigration policies would have the effect of getting net migration down to the tens of thousands. Vince Cable, the business secretary, had said this was not part of the coalition agreement and that Cameron was just talking about Tory policy.

Asked if Cable was right, Clegg told the BBC's The Politics Show: "The result of our immigration policy will lead to a reduction in numbers. It is not government policy to pursue a fixed numerical target."

Lib Dem sources say that an "aim" is not the same as a policy. But the Tories disagree. "Vince Cable was wrong on this," one Tory source said on Sunday. "Theresa May is in charge of the policy on this and she has said innumerable times that the aim of the policy is to bring immigration down to the tens of the thousands."

Cameron and May have not expressed this in terms of a precise target, but their wording suggests that 99,999 is their upper limit for net migration. Andrew Sparrow